1. Field of the Invention
The present invention relates to a communication system with terminal units connected thereto for interchange of voice data, image data, and handwritten data. In particular, the present invention relates to the communication system with the terminal units that allow a user to interchange voice data at the same time to point to image data being transferred.
2. Description of Related Art
Conventional communication systems that implement communications of still image data, handwritten data, and voices employ the following respective techniques.
JP-A No. 1994-284241 describes “telewriting system,” and JP-A No. 2002-330244 describes “voice/image communication system,” both showing such communication systems that handle handwritten data and voices as teleconference systems and multi-function facsimiles.
The telewriting system is so designed as to write graphic patterns and characters on the screen of a terminal unit, which is connected to such a network as a telephone line, the Ethernet (trademark), by using pointing device, distribute the written image data to other terminal units, and thereby display the same images on the screens of those terminal units.
The multi-function facsimile is so designed as to once store a handwritten message scanned by a scanner or a message scribbled on a LCD screen, call for a remote facsimile, and then transfer the stored data to the remote facsimile. The facsimile may also implement voice communications with the remote facsimile during image transmission. In this connection, JP-A No. 1993-327973 describes “telewriting terminal unit” designed so as to display the handwritten data communicated between the terminal units by sequentially overwriting the existing image data.
JP-A No. 1993-063874 describes “handwritten data communication terminals” that shows a system capable of sharing the same data among entire terminal units connected to the system. Specifically, the system allows text data and image data (referred to as Basic Image Data contrasted to Handwritten Data, hereinafter) such as source material used in teaching-learning process or conference use to be shared beforehand among the entire terminal units of the system, and allows a user to specify data needed from time to time depending on the progress of the conferences.
JP-A No. 1993-081592 describes “handwritten data communication terminal units” that allows an original owner of the basic image data to specify a starting location for displaying the data when sharing the data between other terminals.
To cope with conditions where a communication speed is liable to vary dynamically due to an increase/decrease in the number of terminal units and line quality after the line goes through deterioration as time passes, two techniques are explained.
JP-A No. 1996-130514 describes the “image communication terminal unit” designed to make the communication speed stable by dynamically changing the error correction code, as well as the encoding and compressing algorithms used for image communication.
In spite of this technique, there are some cases where degradations of communication state occur and accordingly image degradations advance significantly. To cope with such cases, JP-A No. 1998-079823 describes “image transmission apparatus” in which transferring images is put ahead transferring voices by lowering the voice transfer band and suspending retransmission of missing packets while leaving such packet losses as they are.
While foregoing explanations are about conventional techniques applied in communication systems designed so as to handle image data, handwritten data, and voice data, followings are about problems shown in the afore-mentioned techniques.
“Telewriting apparatus” of JP-A No. 1994-284241 takes no consideration for the performance of a terminal unit and the size of a display screen.
“Voice/image communication apparatus” of JP-A No. 2002-330244 got a demerit for being a facsimile, in which handwritten data therethrough is not real-time one. Thus, the apparatus is unsuitable for real-time communication where, e.g., a user on voice communication can also point to images being transferred in order to add characters and graphic patterns for detailing description as required.
“Telewriting apparatus” of JP-A No. 1993-327973 suffers from its design itself to display the handwritten data communicated between the terminal units by sequentially overwriting the existing image data. Concretely, the apparatus undergoes hardship of deletion of text data and basic image data such as source material used in teaching-learning process or conference use from time to time during the progress of the conferences.
As described above in the system of “handwritten data communication terminal unit” of JP-A No. 1993-063874, the afore-mentioned text data and image data may be shared among entire terminal units connected to the system. Its problems are that contents of those data received by respective terminal units might be different with each other due to an interval of time between time points of receiving the data by the respective units; and that the system is unavailable for real-time communication, suffering from inconvenience of impossibility of correction and replacement of those data.
As described above, “Handwritten data communication terminal unit” of JP-A No. 1993-081592 allows the original owner of the basic image data to specify a starting location for displaying the basic image data when sharing the data between other terminals. However, the unit lacks consideration for a positional link between the basic image data and handwritten data to be written afterward. Therefore, the handwritten data that was written considered for a positional relation to the basic image data might be written differently from what was intended, ending up pointing to a meaningless point.
“Image communication terminal unit” of JP-A No. 1996-130514 suffers from following problems. When the unit dynamically changes the error correction code, as well as the encoding and compressing algorithms, the overhead of the terminal unit increases. Particularly, when an error code with a low bit rate is changed to another with a high bit rate and a high error rate redundancy, the load of the terminal unit increases. Thus, the terminal unit comes to require a high throughput processor and/or expensive processing circuit.
“Image transmission apparatus” of JP-A No. 1998-079823 suffers from following problems. For keeping communication quality stable, lowering the voice transfer band and leaving missing packets as they are and without retransmission of them, cause low quality in voice communication. This might bring about a failure of the voice communication where the voice quality of the remote speaker might be a hardly understandable one.
Under such circumstances, the present invention aims at providing a communication system for enabling such a terminal unit as portable one to make smooth voice communications with another terminal unit by pointing to images using voices, images, and handwritten data.